1. Field of the Invention
The present invention relates to a substrate for diaphragm-type resonant MEMS (Micro Electro Mechanical System) devices, a diaphragm-type resonant MEMS device, and a method for producing the same, and more particularly, to a technology for forming a thin film on a silicon substrate and thereby forming a diaphragm structure.
2. Description of the Related Art
There are known technologies for forming a MEMS device having a diaphragm structure using a SOI (Silicon on Insulator) substrate. In this case, a handle layer and an insulating layer are selectively removed from the back surface of the SOI substrate, and the device layer of the removed regions serves as a diaphragm.
In regard to the method for producing a diaphragm structure using a highly expensive bonding substrate as such, approaches have been taken to produce an equivalent diaphragm structure from a thin film formed on an inexpensive silicon substrate.
For example, JP 2007-129776 A and JP 2010-147658 A disclose methods for suppressing resonant frequency modulation by depositing SiO2, SiN or the like as a diaphragm material on a silicon substrate, and increasing the film thickness accuracy of a diaphragm structure. Also, JP 1999-82777 A (JP-H11-82777A) discloses a gas sensor in which the initial strain of a diaphragm structure has been reduced by laminating SiO2 and SiN.